TWI569362B - Electrostatic clamp - Google Patents

Description

Static fixture

The present invention relates to an electrostatic chuck for holding an object, and a semiconductor manufacturing apparatus including the same.

A lithography apparatus is a machine that applies a desired pattern onto a substrate, typically applied to a target portion of the substrate. The lithography apparatus can be used, for example, in the fabrication of integrated circuits (ICs). In that case, a patterned device (which may be referred to as a reticle or a proportional reticle) may be used to create a circuit pattern to be formed on individual layers of the IC. This pattern can be transferred to a target portion (eg, including portions of a die, a die, or several dies) on a substrate (eg, a germanium wafer). Transfer of the pattern is typically performed via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of sequentially adjacent adjacent target portions.

Known lithography apparatus includes a so-called stepper in which each target portion is irradiated by exposing the entire pattern to a target portion at a time; and a so-called scanner in which a given direction ("scanning" direction) Each of the target portions is irradiated by scanning the pattern via the radiation beam while scanning the substrate in parallel or anti-parallel in this direction. It is also possible to transfer the pattern from the patterned device to the substrate by imprinting the pattern onto the substrate.

Electrostatic clamps can be used in lithographic apparatus that operate at certain wavelengths (e.g., EUV) because at certain wavelengths certain regions of the lithographic apparatus operate under vacuum conditions. An electrostatic chuck can be provided to electrostatically clamp articles such as a reticle or a substrate (wafer) to the respective pieces An object support such as a reticle stage or wafer table. Electrostatic clamping forces can also be used to clamp the electrostatic chuck to the wafer table or other sheet of the lithography apparatus for operation in a two-sided mode.

Conventional electrostatic chucks comprise a stack in which an electrode or a plurality of electrodes are disposed between an upper (first) dielectric or isolation layer and a lower (second) dielectric or isolation layer. For example, if the lower layer is polished, the electrodes are deposited on the upper polished surface. Next, the upper layer is placed on top of the electrode. The upper layer is combined with the lower layer. Each electrode can comprise a plurality of sections. The electrode or electrode portion does not necessarily cover the entire surface of the lower layer. There may be no electrodes in some places. The region between the electrodes or electrode portions may be filled with a barrier (dielectric or insulator) layer or may be empty.

The electrodes can be driven at different voltages such as +3 kV and 0 V or +3 kV and -3 kV, causing an electric field to be generated between the different electrodes. The barrier between the electrodes can withstand a voltage of 3 kV or more. For example, if adjacent electrodes are driven at +3 kV and -3 kV, the barrier between the electrodes will experience a potential difference of 6 kV.

The voltage level at which the barrier can withstand is a factor in its clamping performance. There is a failure mechanism whereby the barrier between the electrodes fails, causing a discharge between the electrodes and a reduction in the clamping force. Any reduction in clamping force can significantly affect the performance of the electrostatic chuck, which can cause a reduction in the yield of the lithography system and cause the output of the integrated circuit to shrink.

For example, it would be desirable to provide an improved electrostatic chuck that gives high clamping force without experiencing significant crash failure rates.

In accordance with an aspect of the present invention, an electrostatic chuck configured to hold an article in a lithography apparatus during use is provided. The jig includes: a lower portion; an upper portion formed of a dielectric material; and a plurality of electrodes disposed between the lower portion and the upper portion. The electrodes include: a first electrode configured to remain at a first voltage during use; at least one intermediate electrode configured to remain in use during use a second voltage; and a ground electrode. The at least one intermediate electrode is located between the first electrode and the ground electrode, and the second voltage is between the first voltage and the ground.

Desirably, the at least one intermediate electrode is maintained at a voltage intermediate the first voltage and the ground during use.

In some embodiments, a plurality of intermediate electrodes may be provided between the first electrode and the ground electrode, and in use, the voltage applied to each of the plurality of intermediate electrodes from the first electrode to the The grounding electrode is reduced. Ideally, the voltage drop between the first electrode and a first intermediate electrode is the same as the voltage drop between adjacent intermediate electrodes.

Ideally, the first electrode and the at least one intermediate electrode share a common power supply, and a resistive network is provided to divide the applied voltage between the first electrode and the at least one intermediate electrode. At least one resistor in the network can be a variable resistor.

In an embodiment of the invention, the fixture is a bipolar clamp, further comprising: a second first electrode; and at least one second intermediate electrode located between the second first electrode and the ground electrode The second first electrode and the at least one second intermediate electrode are respectively maintained at a first voltage opposite to the sign of the voltages applied to the first electrode and the first intermediate electrode, respectively. And a second voltage, and wherein the second voltage applied to the second intermediate electrode is between the first voltage applied to the second first electrode and the ground.

In one embodiment of the invention, the first electrode is generally rectangular and the clamp is configured for use as a reticle holder. In one embodiment, the first electrode is substantially in the shape of a segment of a circle and the fixture is configured for use as a wafer holder.

According to another aspect of the present invention, there is provided a semiconductor manufacturing apparatus comprising an electrostatic chuck as described above.

1‧‧‧Electrostatic fixture

2‧‧‧ plane

3‧‧‧ lower part

4‧‧‧ upper part

5‧‧‧Tumor Festival

6‧‧‧First electrode

6a‧‧‧first electrode

6b‧‧‧second electrode

7‧‧‧Ground electrode

8‧‧‧Voids/Blocks

8a‧‧‧First barrier

8b‧‧‧ second barrier

16a‧‧‧first electrode

16b‧‧‧first electrode

16c‧‧‧Second electrode/intermediate electrode

16d‧‧‧Second electrode/intermediate electrode

17‧‧‧Ground electrode

18 ‧ ‧ barrier

18a‧‧‧Baffle

18b‧‧‧Baffle

18c‧‧‧Baffle

18d‧‧‧Baffle

21‧‧‧Electrostatic fixture

22‧‧‧Substantially fixed plane

23‧‧‧ Lower part

24‧‧‧ upper part

25‧‧‧Tumor Festival

26a‧‧‧First electrode

26b‧‧‧second electrode

26c‧‧‧first electrode

26d‧‧‧second electrode

27‧‧‧Ground electrode / third electrode

28a‧‧‧void/barrier

28b‧‧‧void/barrier

28c‧‧‧void/barrier

28d‧‧‧Baffle

30‧‧‧Voltage supply/electric supply

31‧‧‧First resistor

32‧‧‧second resistor

33‧‧‧ Ground connection

36‧‧‧Second voltage supply

37‧‧‧Resistors

38‧‧‧Resistors

100‧‧‧ lithography device

B‧‧‧radiation beam

C‧‧‧Target section

IL‧‧‧Lighting system/illuminator

M1‧‧‧mask alignment mark

M2‧‧‧Photomask alignment mark

MA‧‧‧patterned device

MT‧‧‧Support structure/pattern support

P1‧‧‧ substrate alignment mark

P ₁ ‧‧‧First clamping pressure

P2‧‧‧ substrate alignment mark

P ₂ ‧‧‧second clamping pressure

P ₃ ‧‧‧Clamping pressure

P ₄ ‧‧‧Clamping pressure

PM‧‧‧First Positioner

PS‧‧‧Projection System

PW‧‧‧Second positioner

SO‧‧‧radiation source

W‧‧‧Substrate

WT‧‧‧ substrate table

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which 1 depicts a lithography apparatus in accordance with an embodiment of the present invention; FIG. 2 depicts a partial cross section of a conventional edge clamp and schematically illustrates a clamp pressure; and FIG. 3 depicts a partial cross section of an edge clamp in accordance with an embodiment of the present invention. Cross-section and schematically illustrates the clamp pressure; Figure 4 depicts a cross section of a conventional clamp and schematically illustrates the clamp pressure; Figure 5 depicts a cross section of the clamp and schematically illustrates the clamp pressure in accordance with an embodiment of the present invention; 6 depicts a partial cross section of an electrostatic chuck according to an embodiment of the present invention, taken along line XX' in FIG. 7; FIG. 7 is a top layer of an electrostatic chuck according to an embodiment of the present invention. Plan view (taken from above); and Figure 8 depicts the clamping pressure applied to the article held by the electrostatic chuck of Figure 7.

FIG. 1 schematically depicts a lithography apparatus 100 in accordance with an embodiment of the present invention. The apparatus includes an illumination system (illuminator) IL configured to condition a radiation beam B (eg, UV radiation or EUV radiation), a support structure or support or pattern support (eg, a reticle stage) MT, Constructed to support a patterned device (eg, reticle) MA and coupled to a first locator PM configured to accurately position the patterned device in accordance with certain parameters; a substrate stage (eg, wafer table) a WT configured to hold a substrate (eg, a resist coated wafer) W and coupled to a second locator PW configured to accurately position the substrate according to certain parameters; and a projection system (eg, A refraction projection lens system) PS configured to project a pattern imparted by the patterned device MA to the radiation beam B onto a target portion C of the substrate W (eg, including one or more dies).

The illumination system can include various types of optical components for guiding, shaping, or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof.

The support structure holds the patterned device in a manner that depends on the orientation of the patterned device, the design of the lithographic device, and other conditions, such as whether the patterned device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterned device, and as will be discussed in more detail below, the present invention relates to an electrostatic clamp. The support structure can be, for example, a frame or table that can be fixed or movable as desired. The support structure ensures that the patterned device is, for example, in a desired position relative to the projection system. Any use of the terms "proportional mask" or "reticle" herein is considered synonymous with the more general term "patterned device."

The term "patterned device" as used herein shall be interpreted broadly to refer to any device that can be used to impart a pattern to a radiation beam in a cross-section of a radiation beam to create a pattern in a target portion of the substrate. It should be noted that, for example, if the pattern imparted to the radiation beam includes a phase shifting feature or a so-called auxiliary feature, the pattern may not exactly correspond to the desired pattern in the target portion of the substrate. Typically, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device (such as an integrated circuit) created in the target portion.

The patterned device can be transmissive or reflective. Examples of patterned devices include photomasks, programmable mirror arrays, and programmable LCD panels. Photomasks are well known in lithography and include reticle types such as binary, alternating phase shift and attenuated phase shift, as well as various hybrid mask types. One example of a programmable mirror array uses a matrix configuration of small mirrors, each of which can be individually tilted to reflect the incident radiation beam in different directions. The tilted mirror imparts a pattern in the radiation beam reflected by the mirror matrix.

The term "projection system" as used herein shall be interpreted broadly to encompass any type of projection system suitable for the exposure radiation used or other factors such as the use of a immersion liquid or the use of a vacuum, including refraction, reflection, Reflective, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof. Any use of the term "projection lens" herein is considered synonymous with the more general term "projection system".

The support structure and the substrate stage may also be referred to as article supports (articles) Support). Articles include, but are not limited to, patterned devices such as reticle, and substrates such as wafers.

As depicted herein, the device is of a reflective type (eg, using a reflective mask). Alternatively, the device may be of a transmissive type (eg, using a transmissive reticle).

The lithography apparatus may be of the type having two (dual stage) or more than two substrate stages (and/or two or more reticle stages). In such "multi-stage" machines, additional stations may be used in parallel, or preliminary steps may be performed on one or more stations while one or more other stations are used for exposure.

The lithography apparatus can also be of the type wherein at least a portion of the substrate can be covered by a liquid (eg, water) having a relatively high refractive index to fill the space between the projection system and the substrate. The immersion liquid can also be applied to other spaces in the lithography apparatus, for example, the space between the reticle and the projection system. Infiltration techniques are well known in the art for increasing the numerical aperture of a projection system. The term "wetting" as used herein does not mean that a structure such as a substrate must be immersed in a liquid, but merely means that the liquid is located between the projection system and the substrate during exposure.

Referring to Figure 1, illuminator IL receives a radiation beam from radiation source SO. For example, when the radiation source is a quasi-molecular laser, the radiation source and the lithography device can be separate entities. Under such conditions, the radiation source is not considered to form part of the lithography apparatus, and the radiation beam is transmitted from the radiation source SO to the illuminator IL by means of a beam delivery system comprising, for example, a suitable guiding mirror and/or beam expander. In other cases, for example, when the source of radiation is a mercury lamp, the source of radiation may be an integral part of the lithography apparatus. The radiation source SO and illuminator IL together with the beam delivery system (when needed) may be referred to as a radiation system.

The illuminator IL can include an adjuster for adjusting the angular intensity distribution of the radiation beam. In general, at least the outer radial extent and/or the inner radial extent (commonly referred to as σ outer and σ inner, respectively) of the intensity distribution in the pupil plane of the illuminator can be adjusted. Additionally, the illuminator IL can include various other components such as a light collector and a concentrator. Illuminator can be used to adjust the radiation The beam has a desired uniformity and intensity distribution in its cross section.

The radiation beam B is incident on a patterned device (e.g., reticle) MA that is held on a support structure (e.g., a reticle stage) MT, and is patterned by the patterned device. After being reflected by the patterned device (e.g., reticle) MA, the radiation beam B is passed through a projection system PS that focuses the beam onto a target portion C of the substrate W. With the second positioner PW and the position sensor IF2 (for example, an interference measuring device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example, to position different target portions C on the radiation beam. In the path of B. Similarly, the first positioner PM and the other position sensor IF1 can be used to accurately position the patterned device, for example, after mechanical extraction from the reticle library or during the scan relative to the path of the radiation beam B ( For example, reticle) MA. In general, the movement of the support structure (e.g., reticle stage) MT can be achieved by means of a long stroke module (rough positioning) and a short stroke module (fine positioning) that form the components of the first positioner PM. Similarly, the movement of the substrate table WT can be achieved using a long stroke module and a short stroke module that form the components of the second positioner PW. In the case of a stepper (relative to the scanner), the support structure (eg, reticle stage) MT may be connected only to the short-stroke actuator or may be fixed. The patterned device (eg, reticle) MA and substrate W can be aligned using reticle alignment marks M1, M2 and substrate alignment marks P1, P2. Although the illustrated substrate alignment marks occupy dedicated target portions, the marks may be located in the space between the target portions (the marks are referred to as scribe line alignment marks). Similarly, where more than one die is provided on a patterned device (e.g., reticle) MA, a reticle alignment mark can be positioned between the dies.

The depicted device can be used in at least one of the following modes:

1. In the step mode, the patterned device (eg, reticle stage) MT and substrate table WT are kept substantially stationary while the entire pattern to be imparted to the radiation beam is projected onto the target portion C at a time (also That is, a single static exposure). Next, the substrate stage WT is displaced in the X and/or Y direction so that different target portions C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.

2. In the scan mode, when the pattern to be given to the radiation beam is projected onto the target portion C, the support structure (for example, the mask table) MT and the substrate table WT (ie, single dynamic exposure) are synchronously scanned. . The speed and direction of the substrate stage WT relative to the support structure (e.g., the mask stage) MT can be determined by the magnification (reduction ratio) and image reversal characteristics of the projection system PS. In the scan mode, the maximum size of the exposure field limits the width of the target portion in a single dynamic exposure (in the non-scanning direction), and the length of the scanning motion determines the height of the target portion (in the scanning direction).

3. In another mode, the support structure (eg, reticle stage) MT is held substantially stationary while the pattern imparted to the radiation beam is projected onto the target portion C, thereby holding the programmable patterning device, And moving or scanning the substrate table WT. In this mode, a pulsed radiation source is typically used and the programmable patterning device is updated as needed between each movement of the substrate table WT or between successive pulses of radiation during a scan. This mode of operation can be readily applied to matte lithography utilizing a programmable patterning device such as a programmable mirror array of the type mentioned above.

Combinations of the modes of use described above and/or variations or completely different modes of use may also be used.

2 depicts a partial cross section of an electrostatic chuck 1 according to the prior art that can be applied to the edges of articles such as reticle or wafer. Figure 2 also schematically illustrates the clamp pressure that can be generated by the clamp by the arrows in the figure. The jig 1 includes a lower portion 3 formed of an insulating material, and an upper portion 4 formed of a dielectric material. The upper portion 4 is formed with a plurality of knob segments 5, whereby the top of the knob segments determines the plane 2 to be held by the article (not shown). The first electrode 6 is provided between the lower portion 3 and the upper portion 4, and the first electrode 6 is adapted to be held at a voltage (typically 3 kV) to generate an electrostatic clamping force. The ground electrode 7 is held at ground and is separated from the first electrode 6 by a gap 8, which serves as a barrier between the first electrode and the ground electrode. The void 8 may be filled with an insulating material, a dielectric material, or may be empty.

The downward pointing arrow in FIG. 2 schematically illustrates the clip that can be generated by the conventional clamp of FIG. Holding pressure. The length of the arrows indicates the clamping force and it will be seen that a uniform clamping pressure can be produced across the width of the first electrode, the magnitude of which will depend on a number of parameters, including applied voltage, dielectric of the upper portion 4. The constant, and the dimensions of the various components of the fixture 1, as will be explained below.

When a voltage is applied to the electrode 6, the article can be held in the plane 2 by an electrostatic clamping force. The electrostatic or capacitive clamping force can be related to the applied voltage according to the following formula:

Where: P _clamp is the clamping pressure applied to the object to be clamped; ε ₀ is the vacuum dielectric constant (8.854×10 ^-12 ); ε _R is the relative dielectric constant of the dielectric of the upper portion 4 of the clamp 1 V is the voltage applied to the electrode 6; d is the thickness of the upper portion 4 of the jig 1; and g is the gap between the upper surface of the upper portion 4 of the jig 1 and the plane 2 to be clamped by the object (the knob 5 Height).

It will be appreciated that the clamping pressure is increased in the region of the knob section due to an increase in the dielectric constant of the knob section relative to the vacuum and an increase in the capacitance in the area. In the area of the knob, equation (1) still holds, however, the thickness d will increase to the height of the knob, and the gap g will be reduced by the same amount, reduced to zero.

A potential problem with this prior art fixture is that there will be a high voltage (eg, 3 kV) across the barrier 8 that can cause the barrier to collapse, which can cause a short between the first electrode and the ground electrode.

Figure 3 is a view similar to Figure 2 but with a clamp 1', and similar components will not be described again, in accordance with an embodiment of the present invention. In the embodiment of FIG. 3, the second electrode 6b is raised. The supply is located between the first electrode 6a and the ground electrode 7. The second electrode 6b, which may be referred to as an intermediate electrode, is held at a voltage between the voltage applied to the first electrode 6a and the ground, and is particularly preferably maintained at about half of the voltage of the first electrode 6a. In the case of the structure of FIG. 3, there are two barrier ribs 8a, 8b - the first barrier rib 8a is located between the first electrode 6a and the second electrode 6b, and the second barrier rib 8b is located between the second electrode 6b and the ground electrode 7. between. As in Fig. 2, the downward arrow indicates the strength of the nip pressure, and as in Fig. 2, there is a uniform nip pressure applied by the first electrode 6a, but in addition, there is a comparison applied by the second electrode 6b. Small clamping pressure. If the second electrode 6b is held at a voltage which is one half of the voltage of the first electrode 6a, the clamping pressure due to the second electrode 6b will be due to a quarter of the clamping pressure of the first electrode, This is because the clamping pressure depends on the square of the voltage.

A potential advantage of the embodiment of FIG. 3 over the conventional structure of FIG. 2 is that because the second electrode 6b is held at a voltage between the voltage of the first electrode and ground, it traverses each of the barriers 8a, 8b. Electric compression reduction. In particular, if, for example, the second electrode is held at a voltage intermediate the voltage of the first electrode and ground, the voltage across each barrier is halved compared to FIG.

Figure 4 shows another form of jig known in the prior art. The fixture of Figure 4 is referred to as a bipolar fixture and includes two first electrodes 16a, 16b that are held at equal but opposite voltages (e.g., electrode 16a can be held at +3 kV while electrode 16b remains at - 3 kV). In all other respects, the two first electrodes 16a, 16b are identical and identical to the prior art fixture of Figure 2, and the electrodes will traverse their width to produce a uniform clamping pressure. However, in the fixture of Figure 4, the potential problem of possible barrier collapse may be even more severe. In the jig of FIG. 4, the two first electrodes 16a, 16b are separated by a single barrier 18, and because the two first electrodes are held at equal and opposite voltages, the potential across the barrier is individually applied. Up to twice the voltage to each electrode (for example, if each electrode is held at +3 kV and -3 kV, the potential is 6 kV).

Figure 5 shows an embodiment of a bipolar clamp 1" according to the present invention. In this embodiment, In addition to the two first electrodes 16a, 16b, a ground electrode 17 positioned to be equidistant from each of the two first electrodes 16a, 16b is also provided, and is disposed between the first electrode 16a and the ground 17b, respectively. Two second electrodes or intermediate electrodes 16c, 16d between the second first electrode 16b and the ground 17b. This structure defines four barrier ribs 18a, 18b, 18c, 18d; the barrier rib 18a is located between the electrode 16a and the electrode 16c, the barrier rib 18b is located between the electrode 16b and the ground electrode 17, and the barrier rib 18c is located between the ground electrode 17 and the electrode 16d, and Finally, the barrier 18d is located between the electrode 16d and the electrode 16b.

It should be understood that the electrodes 16c and 16d are respectively held at the same voltage as the positive and negative signs of the voltages of the electrodes 16a and 16b but having a magnitude between their voltage and ground. For example, if electrode 16a is held at +3 kV, electrode 16c can be held at +1.5 kV, and if electrode 16b is held at -3 kV, electrode 16d can be held at -1.5 kV. Therefore, it will be seen that there is a potential of only 1.5 kV across each of the four barrier ribs 18a, 18b, 18c, 18d, which is formed with the potential of 6 kV across the barrier 18 in the conventional structure of Fig. 4. Comparison.

It should also be noted that in the embodiment of Fig. 5, the second electrodes 16c, 16d contribute to a small clamping pressure as indicated by the smaller arrows in the figure.

Figure 6 depicts a partial cross section (taken along X-X' of Figure 7) of an electrostatic chuck in accordance with an embodiment of the present invention. In the embodiment shown in FIG. 6, the electrostatic chuck 21 is configured to hold the article in the substantially fixed plane 22 in use, and includes a lower portion 23 and an upper portion 24, the upper portion 24 having a knob portion 25, whereby The top of the knobs determines the plane 22 in which the article is held. The first electrode 26a is disposed between the lower portion 23 of the clamp and the upper portion 24. The second electrode 26b and the ground electrode 27 are disposed between the lower portion 23 and the upper portion 24 of the jig 21, but are displaced along the interface between the lower portion 23 and the upper portion 24 such that they do not contact each other or contact the first portion Electrode 26a. The voids 28a, 28b, 28c defining the barrier between the first electrode 26a and the second electrode 26b and between the second electrode 26b and the ground electrode 27 may be filled with an insulating or dielectric material, or may be empty.

A voltage supply 30 can be provided that is configured to supply a voltage to at least a first electrode 26a. The resistor 31 can be configured to couple the first electrode 26a and the second electrode 26b to each other. Additionally resistor 32 can be configured to couple second electrode 26b to ground electrode 27. The ground electrode 27 can be grounded by providing a ground connection 33.

It will be appreciated that the voltage at the first electrode 26a will be substantially similar to the voltage supplied by the voltage supply 30. The voltage at the second electrode 26b will be defined by the ratio of the resistance of the first resistor 31 to the resistance of the second resistor 32, as described in the equation below:

Wherein: V ₂ is the voltage at the second electrode 26b; R ₂ is the resistance of the second resistor 32; R ₁ is the resistance of the first resistor 31; and V _S is the voltage supplied by the voltage supplier 30.

In one embodiment of the invention, the resistance of the first resistor 31 and the resistance of the second resistor 32 are substantially the same. For similar resistors R ₁ and R ₂ , voltage V ₂ will be approximately half of supply voltage V _s . In the case of such resistor values, the voltage (V _s - V ₂ ) between the first electrode 26a and the second electrode 26b will be approximately half of the voltage supplied by the voltage supply 30. The voltage between the second electrode 26b and the third electrode 27 will also be about half of the voltage supplied by the voltage supply 30.

It should be understood that in the case where the intermediate electrode (here, the second electrode 26b) is introduced, the barrier 28 between any two electrodes is subjected to a voltage which is one half of the voltage applied to the first electrode 26a. By reducing the minimum electrical compression that any barrier must withstand by a factor of two, the risk of collapse failure of the barrier is significantly reduced, and as a result, the risk of crash failure of the fixture is significantly reduced.

Figure 7 depicts a plan view of a clamp 21 in accordance with an embodiment of the present invention, a portion of which is It is depicted by the cross-sectional view in FIG. 6. The clamp 21 shown in Figure 7 is of the bipolar form, with a partial cross-section of Figure 6 showing only half of the clamp, especially the left side of the clamp as viewed in Figure 7. The right side of Figure 7 is an equivalent mirror image that differs only in the sign of the voltage applied to the electrodes, as will be explained below. In Fig. 7, the electrode on the left side of the figure has a positive voltage, and the electrode provided on the right side of the figure has a negative voltage.

Referring first to the left side of FIG. 7, first electrode 26a is coupled to voltage supply 30 and is depicted herein as being supplied with a positive voltage relative to ground connection 33. The second electrode 26b surrounds the first electrode 26a and is supplied with a small positive voltage according to a ratio of the first resistor and the second resistor (31, 32) as described by the equation (2), thereby causing the first electrode 26a The barrier rib 28a with the second electrode 26b is subjected to a voltage difference between the first electrode and the second electrode (26a, 26b). The ground electrode 27 surrounds the second electrode 26b and is connected to the ground connection 33. The barrier rib 28b between the second electrode 26b and the ground electrode 27 is subjected to a voltage difference between the second electrode and the ground electrode (26b, 27).

The first electrode 26a may have a size of 145 mm and 35 mm. The width of the second electrode 26b may be between 0.1 mm and 1 mm, for example, 0.3 mm (about 1% of the width of the first electrode), and the second electrode 26b may surround the first electrode 26a, as shown in FIG. Shown. It is conceivable that the width of the second electrode may be as large as the width of the knob segment or the width of the segment of the knob, which may be 5 mm or even 10 mm in the reticle holder. The width of the barrier rib 28a between the first electrode 26a and the second electrode 26b may be 0.7 mm, and the barrier rib 28b between the second electrode 26b and the ground electrode 27 may have a similar size. However, it should be understood that these dimensions are merely illustrative and may vary depending on the particular application. A typical value for a resistor is about 300 ohms (MOhm). When the voltage of about 3 kV is divided by three resistors of 330 mohm, the current is 1 μA and the resistor is dissipated to 1 mW.

The selection of the resistor can be made in consideration of the effect of switching at high speed. While it is beneficial to use current resistors as large as possible to cause current reduction and thus power dissipation reduction, larger resistors will contribute to an increase in response time. For example, the second electrode 26b having the dimensions discussed above will have an area of approximately (145 + 145 + 35 + 35) x 0.3 mm ² or 108 mm ² . The geometric capacitance or capacitance per unit area can be found by the following equation:

Where: C _A is the capacitance per unit area.

All other symbols retain their usual meaning as described above with respect to equation (1).

Under the assumption that the dielectric thickness (d) of 50 microns, the relative dielectric strength (ε _R) is 5 and the knob of the height (g) of 20 microns, the capacitance per unit area (C _A) of 30 pF / cm ² . The electrode of this area will have a capacitance of approximately 32 pF.

It will be appreciated that when switching electrodes between voltages, the resistance of resistor 32 will be combined with the electrode capacitance to produce an RC time constant that will limit the rate at which the electrode voltage can be altered. It may be necessary to make this rise time less than 0.1 second, and ideally less than 0.01 second. If a 32 pF electrode capacitor (as explained above) is used, a resistance of 330 mohm will result in an RC time constant of approximately 0.01 seconds.

The right side of Fig. 7 is a mirror image of the left side and shows a second first electrode 26c surrounded by a second second electrode 26d, wherein the second electrode 26d is surrounded by the ground electrode 27. The barrier rib 28c is defined between the electrode 26c and the electrode 26d, and the barrier rib 28d is defined between the electrode 26d and the ground electrode 27. A voltage is supplied from the second voltage supply 36 to the electrode 26c, and a combination of the resistors 37 and 38 supplies a voltage to the electrode 26d. The ratio of the voltages defines the voltage supplied to the electrode 26d, as by equation (2). description. It should be understood that if the power supply 30 supplies a positive voltage to the electrodes 26a, 26b, the supply 36 will provide a negative voltage to the electrodes 26c, 26d.

FIG. 8 depicts the clamping pressure applied to the item to be clamped in the plane 22. Applying a first pressure P ₁ is sandwiched by the first electrode 26a. A second clamping pressure P _{2 is} applied by the second electrode 26b. The magnitude of the clamping pressure is known by equation (1). Therefore, assuming that the values of the first resistor and the second resistor (31, 32) are substantially equal, the voltage of the first electrode 26a will be twice the voltage of the second electrode 26b. The resulting nip pressure P ₁ applied by the first electrode 26a will be four times the resulting nip pressure P ₂ applied by the second electrode 26b. In the case of the right side mirror, a pressure nip formed equivalents, e.g., an electrode 26c generates the clamping pressure P ₃ and the electrode 26d generates the clamping pressure P _4. Given that the positive and negative sides of the fixture are identical (except for the sign of the applied voltage), then P ₁ will be equal to P ₃ and P ₂ will be equal to P ₄ .

The distance between the upper portion of the clamp 21 and the top of the knob segment 25 can be between 50 microns and 1000 microns, although it should be understood that this size can be selected for any particular application.

Although only two knob segments 25 are shown in Figure 6, it should be understood that in general, multiple knob segments can be used.

In particular, it will be understood from Figure 7 that the clamp shown in the embodiment is substantially rectangular and is therefore particularly suitable as a clamp for a reticle. Embodiments of the present invention are equally applicable to electrostatic chucks for wafers. The fixture for the wafer will typically be circular, and therefore, the first electrodes 26a and 26c will generally be semi-circular in shape, the second electrodes 26b, 26d will be D-shaped, and the ground electrode 27 will be circular. Alternatively, other configurations are envisioned in which a plurality of first electrodes are provided, each of which is a segment of a circle.

The second electrodes 26b, 26d can be regarded as intermediate electrodes in that they are held at a voltage intermediate the voltage of the first electrodes 26a, 26c and the ground. In the case where a single intermediate electrode is provided, it is necessary to maintain the intermediate electrode at a voltage intermediate the voltage of the first electrode and the ground such that each barrier has the same potential across the barrier. However, it is also possible to provide two or more of these intermediate electrodes between the first electrode and ground. For example, two intermediate electrodes may be provided such that there are three barriers between the first electrode and ground. In this case, in order to equally divide the potential across all the barriers, the intermediate electrode immediately adjacent to the first electrode can be maintained at the voltage of the first electrode. And then the second intermediate electrode (immediate to the ground electrode) can be maintained at the voltage of the first electrode . In general, it will be appreciated that a plurality of intermediate electrodes can be used in which a voltage is applied between the intermediate electrodes in a ladder-like manner to produce an equal potential across the barrier thus formed.

It will be appreciated that the presence of a plurality of barriers can be reduced for the area of the electrodes and thus the total clamping force can be reduced. However, this situation can be compensated for by slightly increasing the supply voltage, which will not have to be greatly increased, taking into account that the clamping pressure is a function of the square of the voltage.

In principle, each electrode can have its own power supply to provide the necessary voltage, but this structure will be complex and unnecessarily expensive, requiring an additional high voltage amplifier. Thus, desirably, a plurality of electrodes (all of which are to be provided with voltages having the same sign) are connected to a single power supply, with a resistor network being provided to divide the power supply between the electrodes. This structure can have the advantage of accurate voltage control, for example, there is no possibility of software errors, and the structure is simple and low cost. Possibly, one of the resistors can be a variable resistor to allow for immediate control and adjustment.

In some embodiments of the invention, there may be multiple groups of electrodes, all of which have voltages having the same sign, and in such configurations, it may be desirable to provide each electrode group with its own power supply. And its own resistive network that divides the voltage between the electrodes within the group.

It should also be understood that although the clamping voltages between the display electrodes are only equally divided, non-equal divisions may be used. This situation may enable control of the clamping pressure to provide a shaped clamping pressure rather than a uniform clamping pressure. For example, the pressure gradient at the edge of the clamp can be shaped to achieve a beneficial effect in particular, for example, where there may be a dangling of the supported article, and pressure gradients at the edge may need to be controlled to minimize damage to the article. Risk and / or optimize edge flatness.

In the above description, the ground and ground electrodes have been referred to. However, it should be noted that although a ground electrode is particularly required, it is also possible to use an electrode held at a fixed voltage, and The voltage applied to the first electrode and the intermediate electrode is determined with respect to the fixed voltage.

Although reference may be made specifically to the use of lithography devices in IC fabrication herein, it should be understood that the lithographic devices described herein may have other applications, such as manufacturing integrated optical systems, for magnetic domain memory. Lead to detection patterns, flat panel displays, liquid crystal displays (LCDs), thin film heads, and more. Those skilled in the art should understand that in the context of the content of such alternative applications, any use of the terms "wafer" or "die" herein is considered synonymous with the more general term "substrate" or "target portion". . The substrates referred to herein may be processed before or after exposure, for example, in a coating development system (typically applying a resist layer to the substrate and developing the exposed resist), metrology tools, and/or inspection tools. . Where applicable, the disclosure herein may be applied to such and other substrate processing tools. In addition, the substrate can be processed more than once, for example, to create a multi-layer IC, such that the term "substrate" as used herein may also refer to a substrate that already contains multiple processed layers.

Although the use of embodiments of the present invention in the context of the content of optical lithography may be specifically referenced above, it should be appreciated that the present invention can be used in other applications (eg, imprint lithography) and not when the context of the content allows Limited to optical lithography. In imprint lithography, the topography in the patterned device defines the pattern created on the substrate. The patterning device can be configured to be pressed into a resist layer that is supplied to the substrate where the resist is cured by application of electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterned device is removed from the resist to leave a pattern therein.

Although the use of electrostatic chucks in lithographic apparatus may be specifically referenced herein, it should be understood that the electrostatic chucks described herein may have other applications, such as for reticle inspection devices, wafer inspection devices, aerial image metrology A system, and more generally any semiconductor fabrication system or device, such as a plasma etcher or deposition, for measuring or processing an article such as a wafer or reticle in a vacuum or in a surrounding (non-vacuum) condition. Device.

The terms "radiation" and "beam" as used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (eg, having or being about 365 nm, 355 nm, 248). A wavelength of nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV) radiation (eg, having a wavelength in the range of 5 nm to 20 nm), and a particle beam (such as an ion beam or an electron beam).

The term "lens", as the context of the context permits, may refer to any or a combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components.

The above description is intended to be illustrative, and not restrictive. Therefore, it will be apparent to those skilled in the art that the present invention may be modified without departing from the scope of the appended claims.

21‧‧‧Electrostatic fixture

26a‧‧‧First electrode

26b‧‧‧second electrode

26c‧‧‧first electrode

26d‧‧‧second electrode

27‧‧‧Ground electrode / third electrode

28a‧‧‧void/barrier

28b‧‧‧void/barrier

28c‧‧‧void/barrier

28d‧‧‧Baffle

30‧‧‧Voltage supply/electric supply

31‧‧‧First resistor

32‧‧‧second resistor

33‧‧‧ Ground connection

36‧‧‧Second voltage supply

37‧‧‧Resistors

38‧‧‧Resistors

Claims (11)

An electrostatic clamp configured to hold an article during use, the clamp comprising: a lower portion; an upper portion formed of a dielectric material; and a plurality of An electrode disposed between the lower portion and the upper portion, the electrodes comprising: a first electrode configured to remain at a first voltage during use; at least one intermediate electrode configured to And maintaining a second voltage during use; and a ground electrode, wherein the at least one intermediate electrode is between the first electrode and the ground electrode, and the second voltage is between the first voltage and the ground. The electrostatic chuck of claim 1, wherein the at least one intermediate electrode is maintained at a voltage intermediate the first voltage and the ground during use. The electrostatic chuck of claim 1, wherein a plurality of intermediate electrodes are provided between the first electrode and the ground electrode, and wherein, in use, the voltage applied to each of the plurality of intermediate electrodes is from the first The electrode is reduced to the ground electrode. The electrostatic chuck of claim 3, wherein the voltage drop between the first electrode and a first intermediate electrode is the same as the voltage drop between adjacent intermediate electrodes. The electrostatic chuck of any one of claims 1 to 4, wherein the first electrode and the at least one intermediate electrode share a common power supply, and a resistive network is provided to divide the first electrode and the at least one This applied voltage between the intermediate electrodes. The electrostatic chuck of claim 5, wherein the resistive network comprises a variable resistor. The electrostatic chuck of any one of claims 1 to 4, wherein the clamp is a bipolar clamp The device further includes: a second first electrode; and at least one second intermediate electrode between the second first electrode and the ground electrode, wherein the second first electrode and the at least one are in use The second intermediate electrode is respectively held at a first voltage and a second voltage opposite to the sign of the voltages applied to the first electrode and the first intermediate electrode, and is applied to the second intermediate electrode The second voltage is between the first voltage applied to the second first electrode and the ground. The electrostatic chuck of any of claims 1 to 4, wherein the first electrode is substantially rectangular and the clamp is configured for use as a reticle holder. The electrostatic chuck of any one of claims 1 to 4, wherein the first electrode is substantially in the shape of a segment of a circle, and the clamp is configured for use as a wafer holder. A semiconductor manufacturing apparatus comprising the electrostatic chuck of any one of claims 1 to 9. The semiconductor manufacturing apparatus of claim 10, wherein the semiconductor manufacturing apparatus is one of a lithography apparatus, a reticle detecting apparatus, a wafer detecting apparatus, and an aerial image measuring apparatus.